1. Field of the Invention
This invention relates generally to valves used on large containers of liquids, such as on the holds of river barges, for example, to enable contents of the container to be spilled from the top to avoid development of excessive pressure in the container at any time in general, and during filling operations in particular.
2. Description of the Prior Art
A commonly used approach to limiting internal pressure is to employ a valve which comprises a valve disk mounted on a guide post and which relies on its own weight to keep it sealed in a spill opening on the top of the cargo hold. Several problems are encountered with such an arrangement. For one thing, it is difficult to establish correctly, the internal pressure at which the valve will open. Also, it is difficult to assure adequate spill volume without attendant and excessive internal pressure increases. Also, variations in pressure limits may be encountered as a result of accumulation of dirt, ice or other foreign matter on the valve guide. Also, accumulations of snow or ice on the valve disk may increase its weight to the point where excessive internal pressure will be reached before the valve will open.
It is an object of the present invention to overcome one or more of the shortcomings of the prior art as described above.